1. Field of the Invention
The present invention relates to a method of and an apparatus for filling an image area in a block copy image (an image including characters, illustrations, logos, figures on a base sheet) with a desired color by processing image data representing the block copy image.
2. Description of the Related Art
A block copy, that is, an original including characters and linework to be reproduced, is first prepared in prepress process of a plate for color printing or monochromatic printing. The block copy includes phototype-setting characters and drafted keylines arranged in the same dimensions and quality as final prints, and also has directions for the subsequent reproduction process.
Typical procedure in a prepress process includes: tint laying for uniformly filling a specified area in an image with a desirable color; and coloring characters in the image with a predetermined color. The term `coloring` in this specification implies various coloring processes including tint laying.
Some modern image processing systems have an ability to perform automatic coloring, comprising: an image scanner for reading binary image data of a block copy image; and an image processor for filling a certain closed area or connected area in the block copy image with a desired color on the basis of the binary image data. Conventional image processors perform the coloring processing based on relatively low-resolution image data, which is obtained by scanning an image at a resolution of approximately 400 scanning lines per inch.
Recent technological innovation has allowed the image processing system to process a large volume of image data at a relatively high speed. Accordingly, there has been a strong desire in the field of prepress and printing for an improved system which is able to perform automatic coloring at a high speed on a large volume of image data having a high resolution of approximately 2,000 scanning lines per inch.
The high resolution scanning, however, often causes a large number of pin holes in a binary image. Pin holes are small black dots in a white area of the binary image or small white dots in a black area. The pin holes act as noise components deteriorating the image quality. Since the pin holes are hard to remove after the coloring process, they are required to be eliminated before the coloring process to improve the image quality.
Conventionally, the pin holes are manually eliminated one by one; an operator thoroughly checks an image displayed on a CRT (cathode ray tube) for pin holes and fills each pin hole with the color of an area surrounding the pin hole. This manual processing consumes rather a long time especially when an image includes a large number of pin holes.
Furthermore, since coloring and elimination of pin holes are executed as separate processes, the whole of the image processing requires a considerably long time.